Thanks for these detailled responses .

So, let say I have a Mac 10.4 online. I have the root passwd, and I know it's not changed. I know my user passwd , and i know is not changed.

I've updated Bash. I know what are the services running. 

How could this machine be used to send spam mails ? 

Note: It's not that I don't believe you if you tell it can be done, But please , so far all I read is things scary like "don't go online, it's dangerous"  or "you endanger everyone" and suggestion for cars and motorcycle shoppings. No explanations on how .

Edit: Btw not using a Jaguar Mk2 properly can be very dangerous too… or a fork , or even a teaspoon...